Hydrosilylation chemistry, typically involving a reaction between a silyl hydride and an unsaturated organic group, is the basis for synthesis routes to produce commercial silicone-based products like silicone surfactants, silicone fluids and silanes as well as many addition cured products like sealants, adhesives, and silicone-based coating products. Conventionally, hydrosilylation reactions have been typically catalyzed by precious metal catalysts, such as platinum or rhodium metal complexes.
Various precious metal complex catalysts are known in the art. For example, U.S. Pat. No. 3,775,452 discloses a platinum complex containing unsaturated siloxanes as ligands. This type of catalyst is known as Karstedt's-catalyst. Other exemplary platinum-based hydrosilylation catalysts that have been described in the literature include Ashby's catalyst as disclosed in U.S. Pat. No. 3,159,601, Lamoreaux's catalyst as disclosed in U.S. Pat. No. 3,220,972, and Speier's catalyst as disclosed in Speier, J. L, Webster J. A. and Barnes G. H., J. Am. Chem. Soc. 79, 974 (1957).
Although these precious metal complex catalysts are widely accepted as catalysts for hydrosilylation reactions, they have several distinct disadvantages. One disadvantage is that the precious metal complex catalysts are inefficient in catalyzing certain reactions. For example, in the case of hydrosilylations of allyl polyethers with silicone hydrides using precious metal complex catalysts, use of an excess amount of allyl polyether, relative to the amount of silicone hydride, is needed to compensate for the lack of efficiency of the catalyst in order to ensure complete conversion of the silicone hydride to a useful product. Moreover, when the hydrosilylation reaction is completed, this excess allyl polyether must either be: (A) removed by an additional step, which is not cost-effective, or (B) left in the product which results in reduced performance of this product in end-use applications. Additionally, the use of an excess amount of allyl polyether typically results in a significant amount of undesired side products such as olefin isomers, which in turn can lead to the formation of undesirably odoriferous byproduct compounds.
Another disadvantage of the precious metal complex catalysts is that they risk not being effective in catalyzing hydrosilylation reactions involving certain type of reaction mixtures. Illustratively, it is known that precious metal complex catalysts are susceptible to catalyst poisons such as phosphorous and amine compounds. Accordingly, for a hydrosilylation involving unsaturated amine compounds, the precious metal catalysts are typically less effective than may be desired in promoting a direct reaction between these unsaturated amine compounds with Si-hydride substrates, and will often lead to the formation of mixtures of undesired isomers.
Further, due to the high price of precious metals, the precious metal-containing catalysts can constitute a significant proportion of the total cost of making silicone formulations. Recently, global demand for precious metals, including platinum, has increased, driving prices for platinum to record highs, creating a need for effective, low cost replacement catalysts.
As an alternative to precious metals, certain iron complexes have been disclosed as suitable for use as hydrosilylation catalysts. Illustratively, technical journal articles have disclosed that Fe(CO)5 catalyzes hydrosilylation reactions at high temperatures. (Nesmeyanov, A. N. et al., Tetrahedron 1962, 17, 61), (Corey, J. Y et al., J. Chem. Rev. 1999, 99, 175), (C. Randolph, M. S. Wrighton, J. Am. Chem. Soc. 108 (1986) 3366). However, unwanted by-products such as the unsaturated silyl olefins, which are resulted from dehydrogenative silylation, were formed as well.
A five-coordinate Fe(II) complex containing a pyridine di-imine (PDI) ligand with isopropyl substitution at the ortho positions of the aniline rings has been used to hydrosilate an unsaturated hydrocarbon (1-hexene) with primary and secondary silanes such as PhSiH3 or Ph2SiH2 (Bart et al., J. Am. Chem. Soc., 2004, 126, 13794) (Archer, A. M. et al. Organometallics 2006, 25, 4269). However, one of the limitations of these catalysts is that they are only effective with the aforementioned primary and secondary phenyl-substituted silanes reactants, and not with, for example, tertiary or alkyl-substituted silanes such as Et3SiH, or with alkoxy substituted silanes such as (EtO)3SiH.
Recently new and inexpensive Fe, Ni, Co and Mn complexes containing a terdentate nitrogen ligand have been found to selectively catalyze hydrosilylation reactions, as described in co-pending U.S. Patent Application Publication Nos. 20110009573 and 20110009565, the contents of both publications are incorporated herein by reference in their entireties. In addition to their low cost and high selectivity, the advantage of these catalysts is that they can catalyze hydrosilylation reactions at room temperature while precious metal-based catalysts typically work only at elevated temperatures.
Despite these advances, in view of the high demand for silicone-based products, there is a continuing need in the silicones manufacturing community for other non-precious metal-based catalysts that are suitable for catalyzing hydrosilylation reactions.
The preparation and characterization of several iron and cobalt 2,8-bis(imino)quinoline dichloride complexes have been described by Sun et al. in Organometallics, 2010, 29 (5), pp 1168-1173. However, the catalysts disclosed in this reference were described as suitable for use in the context of olefin polymerizations, not in the context of hydrosilylation reactions.
The present invention provides an answer to the need for additional novel non-precious metal-based catalysts that are suitable for catalyzing hydrosilylation reactions.